Diagnostic Radiology/Musculoskeletal Imaging/Dysplasia Basic/Neurofibromatosis

Neurofibromatosis type I (NF-1), along with Neurofibromatosis type II (a.k.a. MISME syndrome), Tuberous Sclerosis, Sturge-Weber, and Von Hippel-Lindau compromise the phakomatosis or neurocutaneous syndromes, all of which have neurologic and dermatologic lesions. This grouping is an artifact of an earlier time in medicine, before the distinct genetic basis of each of these diseases was understood.

Etiology

Neurofibromatosis type I (NF-1), also known as von Recklinghausen disease, is the result of a defect on Chromosome 17.

Prevalence

1 in 3000-4000 people. Half are caused by new mutations (mutation rate is 1 case per 10,000 population).

Inheritance Pattern

• Autosomal dominant
• 100% penetrance

Mortality/Morbidity

• Mean age of death is 54.4 years, compared to 70.1 for the general US population.
• Malignant transformation of a peripheral nerve sheath tumor is 3-15%.

Diagnostic Criteria

• Need at least 2
  • > 6 cafe au lait spots (larger than 5 mm in children, larger than 15 mm in adults)
  • > 2 pigmented iris hamartomas (Lisch nodules)
  • Axillary, inguinal freckling (Crowe sign)
  • > neurofibroma (or 1 plexiform neurofibroma)
  • optic nerve glioma
  • first-degree relative with NF1
  • dysplasia of greater wing of sphenoid

Radiologic Findings

Radiologic Findings:

• Musculoskeletal: Sphenoid dysplasia (empty orbit sign), pseudarthrosis, ribbon rib deformity, bowing of long bones
• Spine: Kyphoscoliosis in thoracic spine, vertebral scalloping, enlarged neural foramina, lateral thoracic meningocele
• Nerve sheath tumors: neurofibromas (dumbbell lesion), plexiform neurofibroma, malignant peripheral nerve sheath tumor
• GI tract: neurofibromas in stomach and bowel which may lead to obstruction/intussusception, small bowel leiomyoma, small bowel malabsorption
• Eye: Lisch nodules, optic glioma
• Skin: cafe-au-lait spots, cutaneous and subcutaneous neurofibromas, freckling

Extensive neurofibromas involving bilateral sciatic nerves Extensive neurofibromas exiting out the sciatic notch into the peripheral nerves of the right gluteal and thigh muscles

Fig. 1a and b Two images from two different patients demonstrates extensive neurofibromas involving bilateral sciatic nerves (image a), and exiting out the sciatic notch into the peripheral nerves of the right gluteal and thigh muscles (image b).

Large paravertebral soft tissue mass engulfing C6-8 nerve roots Large paravertebral soft tissue mass engulfing C6-8 nerve roots

Fig. 2 Two images from the same patient shows a large paravertebral soft tissue mass engulfing C6-8 nerve roots. Axial image demonstrates tumor extending out the left neural foramen.

Large bilateral neurofibromas involving bilateral lumbar nerve roots, and enlarging the neural foramen. Large bilateral neurofibromas involving bilateral lumbar nerve roots, and enlarging the neural foramen.

Fig. 3 Two images from the same patient demonstrates large bilateral neurofibromas involving bilateral lumbar nerve roots, and enlarging the neural foramen. Axial image demonstrates the so-called dumbbell lesion.

References

• Neurofibromatosis Type 1 by Michael Chang, M.D., University of Washington Department of Radiology
• Neurofibromatosis Type 1